The present invention relates, in particular, to those rotary printing presses in which the printing cylinders of the printing groups each have a groove on their cylindrical surface. This groove extends in the longitudinal direction of the cylinder and is used for the fastening of printing plates, rubber blankets or the like to the surface of the cylinder. In the course of the grooves on cooperating cylinder being overrolled, bending vibrations are generated in the printing cylinders. Such bending vibrations lead to fluctuations in the printing tension in the printing gap. Depending on the size or magnitude of these tension fluctuations, they can result in the formation of stripes in the printed product. The interferences which are caused by such groove overrolling, or groove beats, are all the greater, the wider the groove is.
Changing of the circumferential register of cooperating cylinders of a printing group, or of a printing unit, has an effect on the relative position of the grooves of these adjoining, cooperating printing cylinders, such as, for example, a plate cylinder and a rubber blanket cylinder. In the optimal case of an initial position, the grooves of the two cylinders are located exactly opposite each other. In the case of cylinder grooves of equal width, the effective groove width then corresponds to the actual groove width. In the case of cylinder grooves of differing width, the effective groove width is determined by the width of the wider one of the two grooves. However, if the circumferential register is changed, with respect to this initial position, in the case of certain register settings, a noticeable increase of the effective groove width, and therefore a stronger groove beat, can be produced, which stronger groove beat leads to stronger fluctuation stripes in the printed image.
Depending on the type of printing units, and in particular double printing units on the one hand, and satellite printing units on the other hand, different situations result regarding the appearance of groove beats.
In double printing groups, such as, for example, in bridge printing units, a groove beat occurs, on the one hand, in the rubber blanket cylinder-plate cylinder nip of each printing group, and on the other hand, a groove beat occurs in the rubber blanket cylinder-rubber blanket cylinder nip. In the case of an initial position of the adjustment, or of the setting of the circumferential register of 0 mm, the rubber blanket cylinder groove and the plate cylinder groove roll off each other and are centered. The rubber blanket cylinder groove and the plate cylinder groove, as a rule, have different respective widths. Furthermore, in the rubber blanket cylinder-rubber blanket cylinder nip, the two rubber blanket cylinder grooves, which are typically of respectively the same width also roll off each other and they are centered.
If, in the case of the rubber blanket cylinder-plate cylinder nip, the difference in the groove width between the rubber blanket cylinder groove and the plate cylinder groove is less than twice the maximally possible circumferential cylinder adjustment, an enlargement of the effective groove width will occur at certain register settings.
In the case of a register change, either the relative position, or angle of a rubber blanket cylinder with respect to another rubber blanket cylinder, or the relative position or angle of the rubber blanket cylinder to the plate cylinder changes as a function of the drive concept.
In the case of the rubber blanket cylinder-rubber blanket cylinder nip, and based on identical sizes of the two blanket cylinder groove widths, there is always an enlargement of the effective groove width as soon as the register setting of one of the printing groups deviates from that of the other printing group. This is the result when the two rubber blanket cylinder grooves are no longer located exactly opposite each other.
What has been set forth above will now be illustrated by the use of an example of a web-fed rotary offset printing press. A plate cylinder groove is deemed to be 3.1 mm and the rubber blanket cylinder groove is 4.1 mm. A maximum adjustment of the circumferential register, with respect to its initial position, of 2.5 mm, in both directions, is possible.
First to be considered is a double printing group, in which the circumferential register adjustment is performed via the plate cylinder atone, i.e. wherein the relative position of the rubber blanket cylinder, in relation to the plate cylinder, is changed. In accordance with the prior art, and in connection with a common drive mechanism for the entire bridge printing group, such as, for example, a full depth tooth system this adjustment can be accomplished by an oblique tooth arrangement between the rubber blanket cylinder and the plate cylinder. An axial movement of a gear wheel causes an angular change between the two cylinders. In an initial position, the rubber blanket cylinder groove encloses the plate cylinder groove on both sides with a 0.5 mm difference. In this configuration,the width of the rubber blanket cylinder groove determines the extent of vibratory excitation. This effective groove width changes as soon as the circumferential register is adjusted by more than 0.5 mm. Enclosing of the plate cylinder groove by the rubber blanket cylinder groove now no longer occurs, and the effective groove width increases beyond the width of the rubber blanket cylinder groove of 4.1 mm. At a maximum circumferential register adjustment of 2.5 mm, a maximal effective groove width of 6.1 mm results at the plate cylinder rubber blanket cylinder nip.
On the other hand, if a double printing group is being considered, in which a circumferential register adjustment is accomplished by the use of a common adjustment of the plate cylinder and of the rubber blanket cylinder, the relative position of the two rubber cylinders in relation to each other is changed. In accordance with the prior art, such an adjustment can be accomplished, for example, by the use of software, via the drive mechanism control, by a common drive mechanism for each one of the two rubber blanket cylinder-plate cylinder pairs. In accordance with appropriate considerations, a maximum effective groove width of 8.2 mm results in the rubber blanket cylinder-rubber blanket cylinder nip, with an oppositely equal, respectively maximum circumferential register adjustment in the two printing groups.
What has been said above, basically also applies to satellite printing units, to the extent that the plate cylinder-rubber blanket cylinder nip is concerned. However, the considerations regarding the rubber blanket cylinder-rubber blanket cylinder nip do not play a role here, since the counter-pressure cylinder does not have a groove.
Corresponding to the various drive mechanism concepts, in the prior art the circumferential register adjustment is performed in the following manner:
First, the situation in which all of the printing groups of a printing unit have a common main drive mechanism will be considered. In this configuration, all of the rubber blanket cylinders and the plate cylinders of the printing unit are connected by gear teeth, and thus constitute a full depth tooth system. In this configuration, the circumferential registers are adjusted by changing the respective angular positions of the individual plate cylinders. This, as a rule, is done by making use of an oblique tooth arrangement in the gear teeth. Therefore, the above-discussed groove widening occurs, essentially in the rubber blanket cylinder-plate cylinder nip.
Next, the situation in which each printing group of a printing unit has its own main drive, or has a drive mechanism in pairs will be considered. In such a paired drive mechanism, the rubber blanket cylinder and the plate cylinder of each respective printing group are connected with each other by gear teeth. An adjustment of the circumferential register is performed in this configuration by the use of software via the angular position of the drive mechanism. Thus, in the case of the circumferential register adjustment, both cylinders are turned in the same way. Their relative angular position, with respect to each other, does not change, and thus there is no groove widening.
Finally, the situation in which each printing cylinder of a printing unit, either satellite or bridge has its own main drive will be considered. In this configuration there is an individual drive mechanism for the plate cylinder as well as one for the rubber blanket cylinder. Here, depending on the solution selected in accordance with the prior art, to adjust the circumferential register, either the angular position of the plate cylinder will be changed. The situation explained above, in connection with the full depth tooth system, then results. Alternatively, the angular positions of the plate cylinder and of the rubber blanket cylinder are adjusted together. The situation explained above, in connection with the drive in pairs, then results.
A method for driving a processing machine, such as, for example, a web-fed rotary printing press, is known from WO 2004/028825 A1. Several units, which are free of linear shafts, such as printing groups, for example, and a unit for further processing, such as, for example, a folding apparatus, are independently driven by drive mechanisms. Signals from a guide shaft position of a virtual guide shaft are conducted in a signal line which is connecting the drive mechanisms. An offset is assigned to the respective drive mechanisms, which offset fixes a permanent, but adjustable displacement of an angular target position, with respect to the guide shaft position.
A color register system for a printing press is known from EP 0 598 490 A1, in which printed images are monitored by the use of a camera. The appropriate color intensities are compared with reference color intensities which are obtained from the printing plates, and register deviations are thereby appropriately corrected.
It has also already been proposed, for regulating a register in a printing press, that an image sensor takes an image of a printing substrate which has been imprinted in the printing group of the printing press. This image is then evaluated in an evaluating unit. The evaluating unit generates the actuating command for an actuating drive mechanism, for use in adjusting the register, from a comparison of an actually recorded image with the data obtained from a previously recorded image.
A method for detecting interferences with the transport of a web of material in a web-fed rotary printing press is known from DE 103 38 973 A1. The print-to-cutting register is monitored and, if a preset threshold value is exceeded, a trouble signal is generated.
DE 44 33 905 A1 discloses a method for adjusting a circumferential register of a printing press having at least one printing unit. In the course of this method, the circumferential register deviations of all printing groups are determined, and the printing groups of at least one printing unit are individually readjusted.